JPS61168957A - Bidirectional communication equipment and manufacture thereof - Google Patents

Abstract

An integrated structure for bi-directional optical fiber transmission has a laser diode, a photodetector, and a bi-directional optical waveguide integrated on a common substrate, the waveguide guiding radiation from the laser diode out of the structure and directing incoming radiation of a different wavelength through the structure to the photodetector. The structure also includes a passive optical component cooperating with the strip waveguide for substantially isolating the radiation propagated in one direction in the waveguide from the laser diode, and substantially isolating the radiation propagated in the opposite direction in the waveguide from the photodetector. A method for manufacturing this structure includes essentially growing two epitaxial multi-layer structures spaced from each other and covering selected portions of the substrate constituting the laser diode and the photodetector, with the strip waveguide extending therebetween.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application]: The invention consists of at least one laser diode, at least one photodetector element and at least one passive optical device, especially a wavelength selective device. This article relates to a two-way optical communication device and its manufacturing method.

[Conventional technology]

For example, in a two-way optical communication, in which light of wavelength λ and light of wavelength λ are sent in two transmission directions through a glass fiber, each end of the section has one transmitting element and one receiving element, and two wavelengths. A passive optical device in the form of a selection device is required. This type of equipment is still made in hybrid form and takes an hour and is expensive, making it too expensive for single subscriber use.

In this case, size, stability, manufacturing cost, etc. affect the price.

[Problem that the invention seeks to solve]

The purpose of this invention is to improve this type of device so that it can be produced stably in large quantities at low cost.

[Means for solving problems]

, this object is claimed in claim 1 The configuration mentioned above is achieved by g2.

[Function and effect of the invention]

In order to arrive at the proposal of this invention, which appears to be simple in hindsight, it was necessary to solve the following problem.

In other words, the device which is the object of this invention is a multiplexer, a demultiplexer, and a multiplexer used for two-way optical communication.
In order for the module to have an integrated structure, at least one laser diode, a photodetector element such as a photodiode, a passive optical waveguide, and a passive optical device such as a wavelength selection device must be fabricated on one substrate. These devices pose significant problems because they require significantly different stack configurations and characteristics of each layer.

A method of integrating a DPB laser diode with a striped waveguide has already been proposed (German Patent Application No. 34 36 306), but in this case In0
The main condition is to use the aAsPJiii or Q layer. For the photodiode, a three-component layer of In0aA,s is primarily considered.

The stacked layers made of four component layers and the stacked layers made of three component layers have different layer arrangements and are not aligned with each other, making it difficult to combine such devices on a common substrate. There is a problem.

The present invention provides an epitaxy process with only two epitaxy steps so that as many layers as possible are commonly used in various devices and at the same time it is possible to locally and selectively remove unnecessary layers. It is based on the new knowledge that layers can be grown.

Additionally, the knowledge that despite the apparent discrepancies in double stack systems, many process steps can be performed in common for all devices, thereby reducing the number of process steps. is also used.

In an advantageous embodiment of the invention, a striped or layered waveguide is provided leading from the laser diode via a wavelength-selective grating to the photodetector element, as defined in claim 2. This configuration is advantageous for integrated multiplex-demultiplex modules.

Striped or layered optical waveguide mini-coupled D as a laser diode according to claim 3
It is also advantageous to use an FB laser diode. For the fabrication of a laser diode coupled to a striped waveguide, it is sufficient to add just one auxiliary layer, which will be explained in more detail later.

A particular advantage of the device according to the invention is that it can be produced in only two epitaxy steps. For this purpose, a laser diode, a striped or layered optical waveguide, and a photodetection element are provided on one side of a substrate as described in claim 4, and the photodetection element is provided through a deflection element or It is only necessary to couple it to the optical waveguide by end-coupling.

This deflection element is a type of passive optical device and is realized by structuring a striped or pigeon-shaped waveguide. The end face coupling between the optical waveguide and the photodetector is described in the literature [IEEE Journal of Quant, E
lectr2) QE-13C4], April 1977, p. 220-223C. However, the gaps in the epitaxial covering layer required in this method are unnecessary for the device t of the invention, and the formation of the end-face bond is greatly simplified.

In another embodiment, the laser
Are the diode and optical waveguide on one side of the board? -1 A photodetection element is provided on the opposite surface, and the photodetection element is coupled to the optical waveguide by a deflection element so that the light guided within the optical waveguide is directed from the optical waveguide to the photodetection element via the substrate. be deflected. In this embodiment, since the deflection element is realized by structuring the optical waveguide, the laser
There is an advantage that the manufacturing process of the diode and the optical waveguide coupled thereto, and the manufacturing process of the photodetector element are almost always carried out in tandem with each other. In this case, the substrate must be transparent to the light traveling in the optical waveguide.

Must be.

According to claim 6, a deflection grating formed on or inside an optical waveguide, a reflecting surface placed obliquely with respect to the original propagation direction in the waveguide, or both are used as the deflection element. is also advantageous.

Ru.

In addition to the known end-face coupling, the coupling between the laser diode and the strip-shaped or layered optical waveguide can also be by surface coupling or leakage coupling.

In one advantageous embodiment of the invention, according to claim 7, the laser diode is coupled to the optical waveguide by means of a surface-coupled signal, and at least one end face of the laser diode (: represents the laser beam). A reflective surface is provided which is placed obliquely to the direction of propagation of the laser diode.This reflective surface significantly improves the coupling between the laser diode and the optical waveguide.This reflective surface can be simply etched as an inclined side surface. can be realized.

In the device according to the invention, it is therefore advantageous to use a photodiode or a phototransistor as the photodetector element.

Advantageous embodiments of the multiplex-demultiplex module are disclosed in patent claims 9 to 11.

As previously mentioned, the advantage of the embodiment according to claim 4 is that it can be easily produced with only two embedding steps. One method of carrying out this embodiment is set out in claim 12, the key process steps being the deposition of a layer on a substrate consisting of a laser active layer and an optical waveguide constituent layer which is applied to the C device below. a first epitaxy step on which the layer deposit is removed until it reaches the underlying layer outside the intended area of the laser diode, thereby growing at least three further layers on the exposed surface; This is the second epitaxy process. In this case, the refractive index of the layer forming the optical waveguide is selected to be greater than the refractive index of the medium that follows it and smaller than that of the Radey active layer, and the lowest of the three layers grown in the second epitaxy process is The top layer contains or is superimposed on a region doped in the opposite manner to the 4+2 layer below.

This method differs from known methods only in that in the second epitaxy step only one or more auxiliary layers are formed and receive a specific doping. The uppermost layer of the three layers is for forming a photodetection element and may be undoped, and is doped later by diffusion according to claim 13.

However, instead of the three-layer structure, it is also possible to use ≦multilayers as described in claim 13, one of which is undoped and the other appropriately doped. This double layer can be created in the second Eitakini process.

In this case diffusion is no longer necessary.

If another passive optical device is to be created outside the optical waveguide by structuring the optical waveguide layer, the skin deposit formed by the first epitaxy is partially removed before starting the second epitaxy according to claim 15. After selective removal, the remaining portion is structured to form a passive optical device.

In the method according to this invention 6, the photodetecting element is manufactured according to claim 16, when the uppermost layer of the three-layer structure provided in the second epitaxy is
; removing outside the area intended for the original detection element together with the deposited layers;

An example of a device according to the invention is the integrated multipletas demultiplexing module described above.

Another example is an integrated heterogain or homodyne receiver, where a laser diode and a photodiode are also integrated with other optical devices for optical communication-binary use.

〔Example〕

The invention will now be described in detail by taking an example of an integrated multiplex-demultiplex module containing a DFB laser diode and a photodiode with reference to the drawings.

In the multiplex/demultiplex module shown in FIG. 1, a DFB laser diode l and a striped or layered optical waveguide 12 coupled thereto are connected to layers 11 to 1 provided on the surface of a substrate 1o. = Therefore, it is configured. 3 is a wavelength selection grating, 4 is a polarization grating,
Both are made within the optical waveguide layer lz.

The substrate IO is made of high density N such as 1017S10''.
It is made of in-place doped InP, and layer 11 is made of the same material and has a thickness of 0.5 microns.

Layer 12 is made of a quaternary material such as InGhAsP or In
Although the Q layer is made of GaAlAs, an InGhAsP layer is used in the embodiment shown in FIG.

Is layer 12 the highest density 10I? N-type doping of
The thickness is 0.3 to 0.5 μm, and the fluorescent wavelength is 1.5 μm.
The energy gap corresponding to 3 μm is shown.

The etch stop layer overlying layer 12 may be made of, for example, In.
It is made of P, and its thickness is, for example, 0.1μ, with a density of 101
7 NW doping.

The laser active layer 13 is an undoped, intrinsically conductive layer with a thickness of, for example, O52μ and an energy gap corresponding to the fluorescence wavelength of 155μ.

The layer 14 in which the grating 51 of the DFB radar diode is formed is a P-type C-doped Qll, with an energy gap facing, for example, a 0.3μ corner thickness and a 1.3μ corner fluorescent technology. have. Layer 15 is made of InP;
For example, density 1g+? P-type doping of 1 to 1.
The thickness is 5μ chicken. The layer 16 is made of P with a density of 10''', for example.
It is a +-type C-doped Q layer with a thickness of, for example, 0.2μ and an energy gap corresponding to a fluorescence wavelength of 12μ. Instead of being P-doped, layers 15 and 16 may be N-type 1 doped, for example with a density of 1017.

DFB laser diode 1 is the part placed to the left of stage 52 in FIG. In addition to this, a wavelength selection grating 3, a photodetector element 2 in the form of a photodiode and a deflection grating 4 placed below it are provided.

The photodiode consists of a layer 1 of an undoped ternary material, for example InGaAs, which is applied directly to the surface of the layer 16.
7 and a three-component material layered thereon, such as InGaAa.
It is composed of a layer 18 of. Layer 18 is inversely m+ doped with respect to layer 16 and is Nm in the case of FIG. The thickness of the layer 17 is, for example, 3 μm, and the layer 18 is doped, for example, in the N type with a density of 10 and the thickness is, for example, 0.2 μm. The doping of the layer weight 8 can be P type with comparable density.

In order to ensure that the light guided in the striped or layered optical waveguide reaches the photodiode 2c, a deflection grating 4 is made in the layer 12 below this photodiode, directing at least part of the light to the photodiode 2c. Deflect towards 2.

A wavelength selective grating 3, which constitutes the actual demultiplexer, is formed in the layer 12 between the laser diode l and the photodiode 2, the parallel grooves of which are parallel to the layer 12 and perpendicular to the plane of the paper of FIG. A car is moving in a certain plane against this page.

This grid 3 constitutes the actual multiplexer and demultiplexer of the module.

In the module of FIG. 1, the contacts necessary for the operation of the photodetector elements of the laser diode are provided on layer 16 in the area of the laser diode 1 and on layer 18 in the area of the photodiode. has at least one contact on board 1
0C is provided.

Details 1 of the manufacturing method of the module shown in FIG. 1: Before going into detail, the function will be briefly explained. A part of the electromagnetic radiation of wavelength λ generated by the laser diode l enters the optical waveguide 12C placed below the laser active layer 13 as a leakage wave and reaches the wavelength selection grating 31; it reaches the integrated photodetector. Reaching element 2 is prevented. Electromagnetic radiation of wavelength λ, traveling in the opposite propagation direction, is introduced from the glass fiber into the optical waveguide 12 and guided by the wavelength selection grating 3 to the photodetector element 2C. The grating 3 in this case prevents light of wavelength λ from reaching the radar diode IC.

The main parts of the manufacturing process for the module shown in FIG. 1 are as follows. First, in a first epitaxy process, the layers 11 to 14 of the surface 62 of the substrate 10 are completely deposited, and then the layers 13 and 14 are selectively removed outside the intended area of the laser diode to form a step 52. Various gratings 51° 3 and 4 are subsequently created on this stepped surface. In this case, these grating structures are formed in layers 12 and 1 after irradiation of the predetermined areas with laser light or an electron beam in one or more process steps.
Created by etching 4. This etching can be performed commonly for all grating structures. In the following 1::'lFJ nievitaxy process, a stepped surface in which a grating structure is etched is formed in layers 15 to 18. Subsequently, layers 17 and 18 are selectively removed outside the area of photodetector element 2.

Finally, the metal contacts necessary for the operation of the laser diode l and the photodetector element 2 are provided. The subsequent steps are layers 13 and 1.
After the selective etching of 4 and before the second epitaxy step, the layer 12 is structured such that the second epitaxy step ≦2 and 3
There is almost no difference from the conventional method except that the above layers are created and the auxiliary layer is selectively removed.
Other differences are not essential.

FIG. 2 shows the diamond shape of the unit of FIG. In this modification, since the substrate 10 is semi-insulating, the photodetecting element 2
In addition to requiring a contact, shown as 160, in layer 16 as well as layer 18, layer 12 must be doped to the same conductivity type as layers 15 and 16. Similarly, for the laser diode layer 12 or 11 (=
A contact is provided.

In the module of FIGS. 1 and 2, both auxiliary layers 17 and 18 are provided in a second epitaxy step, layer 18 serving as the dopant source for the doping required for the formation of the photodiode contacts. However, this dopant is in the undoped layer 1
You can also set it to 7. In the modification shown in FIG.
0 and layer 11 are doped with Nff1l:, making them conductive. Layers 12, 15 and 16 are N-type doped. Layer 17 is undoped, but on the opposite side CP! with respect to substrate 10! II! + A doped region 170 is created by local diffusion 6:. This area 17G
is a substitute for the layer 18C in FIG. 1, 'W42. 19
is a covering layer and at the same time is used as a diffusion mask. Layer 19 is provided after selectively removing layer 17 and layer 1
Diffusion material can be introduced through the hole for the remaining portion of 7. Also, the P type C doped region 170
It is also possible to make a C contact.

! ! In the module of FIG. 3, layers 12, 15 and 16 are the first factor, as in the module of FIG. With such a doping type, in the area of the laser diode I, the layers 14 and 15 must be doped, for example by diffusion, to a deep depth so that they are completely P-type.

FIG. 4 shows an alternative embodiment of the first (l) module.
Fig. 3 shows a form corresponding to the third factor.

In this embodiment, an end-face coupling is created between the optical waveguide 12 and the photodetector element 2. For this purpose, after the first epitaxy step and before starting the second epitaxy step, the deposition of the layers 11 to 14 provided by the first epitaxy as well as the structuring of the layer 12 and the localization of the substrate to a certain depth in the area where the photodetector element is to be provided are carried out. An auxiliary process step is required to remove the Substrate 10
The depth t for removing a portion of is selected such that the layers 12 and 17, with the layers 15, 16, 17 and optionally 18, are aligned at the same height 1: in the intended area of the photodetector element 2.

The light that propagates in the layer 12 from the grating 3 toward the photodetector element 2 exits from the end face 121 of the layer 12 made in the auxiliary process step, and in front of it, the light propagates in the vertical direction (= penetrating the expanding portions of layers 15 and 16). and are incident on layer 17 placed at equal height.This module does not require a deflection grating.

Modification of the coupling from the radar active layer 13 to the optical waveguide 12 II
Reflective surfaces layered diagonally can be used. This reflective surface can be easily realized by making the step 52 in the other units in FIG. 1 an inclined surface.

Top view of Figure 5 6 = In the multiplex-demultiplex module shown, the laser diode l
and the photodetecting element 2 are simply shown as squares. The structured optical waveguide consisting of the layer 12 of FIGS.
, and a striped optical waveguide section 122 that branches off from the striped optical waveguide section 120 to reach the photodetector element 21 . This branched optical waveguide section 122 is directly in contact with the optical waveguide section 120-.

In the branch area 123 the structured striped waveguide 12
A wavelength selective grating 3 having an extent at least equal to the width b of the optical waveguide section 120 is provided as a deflection element. Fifth
Plane 1 of the figure: grating stripes 31 consisting of, for example, grooves extending in parallel are placed obliquely to both the light propagation direction R in the waveguide section 120 and the light propagation direction R8 in the branching optical waveguide section 122. ing.

The tilt angle of the grating stripes 31 of the deflection grating 3 and its grating constant are determined by the wavelength λ1 emitted from the laser diode l.
, which travels in the waveguide section 120 past the branching waveguide section 122 to the edge of the substrate 10 and is emitted from there, is incident on the tapered tip 81 of the glass fiber 8, and is incident on the tapered tip 81 of the glass fiber 8. 8 to the waveguide section 120 is deflected toward the branching waveguide section 122C and guided to the photodetecting element 2.

In this case, no significant portion of the light of wavelength λ will be transmitted to the photodetection confection, nor will a significant portion of the light of wavelength λ reach the laser diode 1.

The multiplex-demultiplex module shown in FIG. 6 differs from that of FIG. 5 primarily in that a wavelength-selective directional coupler is used instead of the wavelength-selective branching grating 3. The laser diodes and photodetection elements are identical in FIGS. 5 and 6 and are both shown as 1 and 2.

The same applies to the glass fiber 8 having a tapered tip.

Striped optical waveguide 120 terminating at end face 1210 in FIG.
0 corresponds to the striped optical waveguide section 120C ending at the end face 121 in FIG. 5, and the optical waveguide section 1220 in FIG. 6 corresponds to the optical waveguide section 122 in FIG.

The striped branch optical waveguide section 1220 is the branch section fi1.
A striped optical waveguide section 1200 through which a wavelength-selective directional coupler simultaneously serves as a deflection element at 230
is optically coupled to. Both striped waveguide sections 1200 and 1220 are therefore parallel and closely spaced by a certain length in the branching section 1230, allowing light of wavelength λ, to be coupled, but not light of wavelength λ, from laser diode 1. are designed to be uncombinable.

Striped optical waveguide sections 1200 and 1220 together with directional coupler 30 constitute a structured striped optical waveguide, which is realized by dove 12 in FIGS. 1-4.

[Brief explanation of drawings]

FIG. 1 shows a cross section parallel to the light propagation direction of a multiplex/demultiplex module according to the present invention,
FIGS. 2, 3 and 4 each show a preferred embodiment of the invention, while FIGS. 5 and 6 are plane views of a multiplex-demultiplex module according to the invention. In FIG. 1, 1...DFB laser diode, 2...Photodetection element, 3...Wavelength selection grating, 4...Polarization grating, 10...Substrate. IG 2 IG 3 FIG 4 FIG 5 FIG 6

Claims (1)

[Claims] 1) The laser diode (1) and the photodetector element (2) are integrated on one common substrate (10) together with the striped or layered optical waveguide ((12), passive At least one laser device characterized in that the optical device is realized by a striped or layered optical waveguide (12) itself or by a particular structured form thereof (3, 30, 4) or both. A two-way optical communication device consisting of a diode, a photodetector element and a passive optical device. 2) From the laser diode (1) to the wavelength selection device (3) which constitutes the passive optical device and then to the photodetector element (2). Striped or layered optical waveguides (
12). The device according to claim 1, characterized in that it comprises: 3) Device according to claim 1 or 2, characterized in that the laser diode (1) is a DFB laser diode coupled to an optical waveguide (12). 4) The laser diode (1), the optical waveguide (12) and the photodetector element (2) are provided on the same side of the substrate (10), and the photodetector element (2) is provided on the same side of the substrate (10); 4. Device according to claim 1, characterized in that it is coupled to the optical waveguide (12) by end-coupling. 5) The laser diode and the optical waveguide are provided on one side of the substrate, and the photodetector element is provided on the opposite side, and the photodetector element is coupled to the optical waveguide through a deflection element so that the light guided through the optical waveguide is 4. Device according to claim 1, characterized in that it is deflected from the optical waveguide through the substrate towards the photodetector element. 6) The deflection element is composed of a deflection grating (4) formed on or inside the optical waveguide (12) and/or a reflective surface placed obliquely to the propagation direction of light in the optical waveguide. A device according to claim 4 or claim 5 characterized by: 7) The laser diode (1) is coupled to the optical waveguide (12) through surface coupling, and at least one end face of the laser diode is provided with a reflective surface placed obliquely to the direction of laser light propagation. Device according to one of the claims 1 to 6, characterized in that: 8) The device according to any one of claims 1 to 7, characterized in that the photodetecting element is a photodiode or a phototransistor. 9) a striped waveguide section (120) in which a structured striped optical waveguide (12) extends from the laser diode (1) to one edge of the substrate (10) and terminates there;
.
1230) is provided in the branching section (123, 1230), this element allows the light of a specific wavelength (λ_1) emitted from the laser diode (1) to be directed to the edge of the substrate (10) where the optical waveguide (12) terminates. Light of a specific wavelength (λ_2) guided to the end portion and incident on the optical waveguide section (120, 1200) from the edge portion of the substrate is directed to the branch waveguide section (122, 12).
20) and guided to the photodetection element (2), at which time a large part of the light with wavelength λ_1 is not guided to the photodetection element (2), and a large part of the light with wavelength λ_2 is deflected by the laser diode (2). Claims 4 and 6 are characterized in that they are configured so as not to reach 1).
Apparatus according to one of paragraphs 7 or 8. 10) The branching striped waveguide section (122) is directly in contact with the striped waveguide section (120), the deflection element (3) being on the structured striped waveguide (12) in the waveguide branching section (123). a wavelength-selective polarization grating provided in the waveguide section (120) and occupying at least the width of the waveguide section (120), the grating stripes occupying the width of at least the waveguide section (120);
Inside optical propagation direction (R_1) and branch waveguide section (122)
Claim 9, characterized in that the lattice constant is selected such that it is inclined with respect to both the light propagation direction (R_2) in the second specific wavelength λ_2 and that only the light of the second specific wavelength λ_2 is deflected.
Apparatus described in section. 11) that one branch stripe waveguide section (1220) is coupled to another stripe waveguide section (1200) through a wavelength selective directional coupler (30) which constitutes a deflection element in the branch section (1230); 10. The apparatus of claim 9. 12) In the first epitaxy process, the laser active layer (
13) and an optical waveguide-forming layer (13) therebelow, on the surface of the substrate (10), and this superimposition layer is formed on the surface of the substrate (10), except for the area intended for the laser diode. ), whereby the exposed surface is grown in a second epitaxy step with at least three layers (15, 16, 17), with no boundaries between the underlying layers (12). The layer (15) in contact with the layer (12)
a refractive index smaller than A method for manufacturing a two-way optical communication device comprising a laser diode, a photodetection element, and a passive optical device. 13) Second layer (16) following the top layer (17) of the three-layer structure
A patent claim characterized in that the dopant is diffused into the top layer (17) with respect to the doping of the region which is doped inversely to the top layer, such that the diffusion area occupies only a part of the thickness of the top layer. The manufacturing method according to item 12. 14) Layer (16) following the top layer (17) of the three-layer structure
Claim characterized in that the oppositely doped region with respect to the doping of is formed by adding a correspondingly doped layer (18) onto the layer (17) during a second epitaxy step. The manufacturing method according to item 12. 15) selectively removing the stack of layers produced in the first epitaxy step up to the bottom layer (12) before starting the second epitaxy step and then structuring this layer (12) for forming a passive optical device; The manufacturing method according to claim 12, characterized in that: 16) the area where the top layer (17) of the superimposed layer provided in the second epitaxy step, optionally together with one or more layers provided above, is intended for the photodetector element (2); 16. Process according to claim 12, characterized in that the material is selectively removed outside of the.